Intel NUC - Intel NUCs are available as Kits(Barebones), Boards(Mainbaord only) and as perconfigured Mini-PCs.
Intel NUC boards - Four-by-four inch Intel NUC boards come with a soldered-on processor.
Olimex A64-OLinuXino - Open source hardware board that runs Linux and Android. Entirely designed with open source software CAD tools.
ESPRESSObin - Electronics, Single Board Computer, and x86
esp32 - A very cheap small chip, compatible with Arduino.
Qualcomm DragonBoard - https://developer.qualcomm.com/hardware/dragonboard-410c